The Keystone meeting on "Molecular Mechanisms of Leukocyte Trafficking" will be a comprehensive gathering of the world's foremost scientists working in a cutting-edge basic science area with important ramifications for human disease. This meeting is a reprise of a highly successful joint meeting on "Molecular Mechanisms of Leukocyte Trafficking" and "Endothelium" held in March 1998. The past few years have seen continued advances in the understanding of how leukocytes extravasate and migrate within tissues. There has been further elucidation of the participation of: selectins and their ligands; chemokines and their receptors; integrins; and Ig superfamily molecules. A number of novel strategies for anti-inflammatory therapeutic have already emerged from these disciplines and more are likely to follow. The meeting will bring together scientists working in diverse range of topics in leukocyte and vascular biology. The resulting interactions are likely to stimulate new approaches to the critical remaining problems in trafficking research.